Power tools, for example, power garden tools having long shafts, present interesting and, at times, subtle challenges in their assembly and use.
As one consideration, providing for compact storage and shipment, quick and convenient assembly and sturdy, long-term operation under sometimes extreme conditions, brings to bear requirements which, to a significant extent, tend to be contradictory. In this regard, Hampel, U.S. Pat. No. 4,397,088, is illustrative.
Hampel specifically provides for a two-piece hollow handle having pieces which are held together by a sleeve having semi-circular halves. In assembly, the handle pieces are telescoped and the sleeve halves are joined using, e.g., screws and bolts. Protrusions (lugs) along the inside of the sleeve halves fit in holes along the telescoped handle pieces. The protrusions, along with abutting sleeve halves, are stated to be clearly preferred, due to sturdiness requirements, over the conceptually adverted to alternative of utilizing gripping action provided by joined sleeves (column 3, lines 37-54, and column 4, lines 24-32).
Somewhat related to this, for example, on tools using a long flexible shaft and a two-piece handle joined without telescoping the handle pieces, other forms of internal protrusions have been employed. According to one form, a circumferentially elongated protrusion along the inside of one of the sleeve halves is received in a similarly circumferentially extending opening in the lower handle piece. For the top handle piece, there would typically be a lug or pin-like protrusion (key) and a hole to closely fit about such protrusion. A single wing screw, at the lower end of the sleeve, for example, has been employed to somewhat speed the assembly and disassembly process. However, it is evident that, so far as this is concerned, from a practical standpoint, there is little difference between this and what is shown in Hampel. Moreover, with the circumferentially extending protrusion and opening, typically, some room is left for rotation of the lower handle piece and operating head of the tool with respect to the upper handle piece, for example, if the operating head bumps into an object. This, however, is considered to be a substantial detriment from the point of view of sturdiness and safety.
Yet further, along somewhat similar lines, two-piece shafts, in the past, have been found useful in power tools of various varieties, including garden tools.
With regard to holding or joining mechanisms along the general lines shown in Hampel and discussed above, consideration and effort has gone into incorporating quick-change features - i.e., attempting to provide for quick substitution of different operating heads with regard to a single operator end of a tool. One such proposal would employ a pin or lug-like protrusion along the inside of a sleeve piece to be received in an L-shaped ("bayonet") opening having a long leg opening at the upper end of a non-telescoped lower handle piece, and utilizing the single wing screw noted above. This approach, so far as known, has not been adopted. Disadvantages relating to ease and quickness of connection and disconnection of the head and rotation of the head end with regard to the user end, e.g., upon bumping into an object, as explained above, remained.
With regard to changing alternative tool heads, although related to general tool assembly, additional important considerations come into play. Specifically, ease and rapidity are enhanced in importance because the operation may be repeated hundreds of thousands of times during the life of the tool rather than merely, e.g., after initial shipment, long-term storage or repair. Related to this is the desire for simplicity, not only to contribute to such rapidity, but also to avoid mistakes which are much more likely to crop up in the hundreds or thousands of changes over the life of the tool. Such mistakes, at a minimum, can eliminate the sturdiness required for effective operation, and, at the other extreme, present a grave danger to the operator or some other individual in the vicinity of the tool.
Considered in a somewhat broader framework, the present situation involves several areas of concern. It generally involves mechanical interfacing which is employed in the connection of parts that rotate with one another during operation. It also generally involves the joining of parts through sleevelike devices.
As to this framework, and the interfacing aspect, Walker, U.S. Pat. No. 3,080,185, provides a mechanism for assembling a radio face plate with a knob thereon on a radio chassis, even though the part, on the chassis, which the knob is to control, is not turned to the position required for connection with the knob mechanism. The connection mechanism incorporates a spring-loaded part which, ultimately, receives the part on the chassis which is to be controlled by the knob. Thomas, U.S. Pat. No, 1,695,564, Zaleske, U.S. Pat. No. 2,327,951, and Cadwallader, U.S. Pat. No. 2,425,992, show other spring-loaded connection mechanisms. In Thomas, apparently, correct rotational positioning is achieved by hand in a tool which can be either hand-driven or power driven. Zaleske and Cadwallader are of more limited interest and particularly relate to interconnection for control purposes.
Concerning such broader framework, and the sleeve-related aspect, Thomas, U.S. Pat. No. 907,539, provides sleeve halves, for joining two shafts which are to rotate with one another. Opposing inner surfaces, along each of two sleeve halves, are separated by less than the diameter of the shafts to provide pressure points against the shafts as the halves approach one another and are bolted to one another on the shafts. Near the pressure points, the inner surfaces of the sleeve halves have curvatures which substantially follow the curvature of the shafts. However, away from these points the inner surfaces recede from the shafts to provide spaces between the shafts and such inner surfaces.
Wuelker, U.S. Pat. No. 1,636,087, employs wing screws with respect to sleeve-like holding devices. It also employs various ways of connecting shafts, including split bushings; employs a flexible shaft with a sheath; and employs a tubular handle. Priest, U.S. Pat. No. 501,731, somewhat similarly, employs wing set screws with respect to a tubular sleeve associated with the connection between flexible and rigid shafts.
Murdock, U.S. Pat. No. 713,135, employs bolted-together, in the nature of sleeve portions, in conjunction with elongated triangular-shaped members, to frictionally hold two shafts.
Barker, U.S. Pat. No. 3,583,356, and Grace, U.S. Pat. No. 455,396, provide two-piece sleeves which are screwed or bolted together in joining two shafts, in the case of Grace, a rod-like and a flexible shaft. Firth, U.S. Pat. No. 3,068,665, Schwemlein, U.S. Pat. No. 1,656,992, Gay, U.S. Pat. No. 736,378, Tapley, U.S. Pat. No. 1,677,375 and MacKenzie, U.S. Pat. No. 3,851,983, also are of some, albeit limited,interest.
The present invention provides for compact storage and shipping of a tool, e.g., a garden tool with a long shaft. It also provides for rapid assembly and rapid substitution of alternative tool heads without any need for concern with split-shaft coupling by the user in such assembly or substitution. Along with such rapid assembly and substitution, it maintains great sturdiness of connection during operation. It accomplishes the foregoing in the detailed connecting interface between split-shafts and in the detailed clamping features for securing the user end and operating heads end of the tool.